Photochromic materials change colors reversibly with irradiation of light and suitable for various applications such as optical recordings, optical switches, modulators, and the like. Investigations have been performed to develop novel photochromic materials which are applicable for optical information recoding medium capable of reproducing information signals or recording and reproducing information signals by using light beams.
Irie et al. have reported processes for preparing photochromic diarylethene compounds, which have excellent photochromic property and durability, and their uses (Masahiro Irie, Chem. Rev., 2000, 100(5), 1685–1716). However, these photochromic diarylethene compounds have a drawback such as gradual erasing of the record due to poor fluorescent property.
In order to be free from the above problem, Lehn et al. have developed dithienylethene-tungsten compounds having fluorescent property (Fernandez Acebes A, Lehn J. M., Advanced Materials, V.10 N.18, 1519, 1998). However, it has another drawback that a short wavelength of 240 nm has to be irradiated to these compounds to exhibit fluorescence. In other words, it requires high energy.
Irie et al. have also developed fluorescent diarylethenes substituted with diporphyrin or triphenylimidazole (Journal of Organic Chemistry, V.66 N.16, 5419–5423; V.66 N. 11, 3913–3923, 2001). However, these compounds has poor photochromic property and low solubility, thus being inapplicable for manufacturing thin film thereof.